XCR new configuration, round 2

[Martens]

I got my PDW upper today and got a chance to head to the range. The temp was 62 degrees and the rain varied from a mist to a steady, medium rain. All ammo was wolf 55 grain.

The goal was to swap my 14.5 inch barrel with fixed muzzle attachment and make a lighter, better balanced gun, without having to go through NFA paperwork.

At the range, I fired a control group at 50 yards out of my XCR with the standard upper. I was still zeroed. I swapped the barrel, gas tube, and bolt to the new upper and fired a group. This group was the same size, but 2 inches low and 2 inches right. The necessary scope adjustments were made and a final group was fired and it was dead center.

I continued to work the gun firing a total of 40 rounds in the new configuration. Felt recoil was a little more, but I figured that as weight was down. I noticed that ejection was not as far as with my old upper but I would imagine that is a result of the new upper being dry and needing to wear in with the bolt.

Functioning was 100%. I fired from 100 yards and in, from prone, kneeling, and standing. The new configuration definitely feels more lively. Holding it steady in the unsupported position was a lot easier. You could feel the difference in carrying it as I walked to each distance.


I tried to come up was a way to determine how much the center of gravity moved rearward but could not come up with repeatable results. The gun definitely is less front heavy. Looks are subjective, but the exposed gas tube is growing on me. For me, I did not give up any useable rail space as the light and VFG are the same distance from the mag well as before and apparently I was not using the forward portion for anything but mounting a bipod.

Pics coming soon.

[WatchoutforStobor]

Congrats! Look forward to the pictures.


Are you the one who originally requested the configuration from Robarms?

[Martens]

I didn't request the configuration, but I am glad it is doable. Here are some pics of the new, lighter configuariton with my SPR style XCR. I also took some pics of the new style with a fixed CTR stock.

[Sean K.]

That looks great man. This new configuration is really starting to grow on me. Your SPR build looks really nice too.....I like how low the optic is mounted.

Sean

[TerraShrewsbury]

That looks great man. [b]This new configuration is really starting to grow on me. Your SPR build looks really nice too.....I like how low the optic is mounted.

Sean

quoted for later reference. 8)

[Sean K.]

That looks great man. [b]This new configuration is really starting to grow on me. Your SPR build looks really nice too.....I like how low the optic is mounted.

Sean

quoted for later reference. 8)

Hey, I already have the order in for a 9" 5.56 PDW upper.... Since I'm gonna have a regular upper laying around....I can make this configuration pretty easily.

[variablebinary]

The XCR-SF is full of so much win!

[jon1371usmc]

Its starting to grow on me. Doesnt really matter to me much, as I already have a full size upper so I am stuck with it. I still think it would look better with a gas block mounted front sight though.

[Martens]

I tried to get both scopes mounted as close to the same height above bore as I could. The Trijicon on the XCR-SF is a 30 mm tube in Burris 1/2 rings for a scope center height of 1.09 inches. The IOR on the SPR has a 35 mm tube in 1/4 rings for a centerline height of .93 inches. The 1/16 difference between the two is not noticeable.

Believe it or not, a 30 mm tube RDS in the 1/2 inch mounts will also co witness with standard AR BUIS's. The witness is in the upper portion, but it does work. The new low height irons should be right around a perfect co witness.

These mount combos give me a cheek weld slightly tighter than an AR. It is very positive and comfortable.

[MartinRiggs]

I'd like to get one with the barrel gas port moved inboard.

I guess Rob Arms could do that since they drill the gas ports in house.